1. Field of the Invention
The present invention relates to a toner supplying roller provided in the developing apparatus of an image forming apparatus, such as a copying apparatus, an image recording apparatus, a printer and a facsimile, and a method for manufacturing the same.
2. Description of the Related Art
An image forming apparatus, such as a copying apparatus, an image recording apparatus, a printer and a facsimile, includes a developing apparatus that develops an electrostatic latent image formed on a latent image bearing member, such as a photosensitive member and an electrostatic recording dielectric. The developing apparatus includes a developer container that stores a toner (a developer), a developing roller that is provided with its part exposed from this developer container to block the opening of the developer container, and a developing blade that abuts the developing roller and forms a toner thin film having a constant thickness on the developing roller. The toner is friction charged when passing between the developing roller and the developing blade with the rotation of the developing roller, conveyed to the opposing latent image bearing member in the portion where the developing roller is exposed from the developer container, and moved to an electrostatic latent image having higher potential, for development.
In such a developing apparatus, a toner supplying roller that scrapes off the toner not used for the development of the electrostatic latent image and remaining on the surface of the developing roller and supplies a new toner in the developer container onto the developing roller is provided in the developer container. The development residual toner scraped off from the developing roller is mixed with the toner in the developer container, and the charge of the development residual toner is diluted and disappears.
This type of toner supplying roller needs to have low hardness or flexibility and the conveyance property that enables the conveyance of a large amount of the toner, to remove the development residual toner and supply a new toner smoothly between the toner supplying roller and the developing roller. Therefore, a polyurethane foam layer formed of a foamed elastic member, such as a polyurethane foam, or the like is provided on the surface of the toner supplying roller, as one that is flexible and has apertures. For example, a polyurethane foam in which toner supply to and toner scraping off from the developer carrier are uniform (Japanese Patent Application Laid-Open No. 2004-037630), a conductive polyurethane foam member having stable fine cells (Japanese Patent Application Laid-Open No. 2002-363237), a semiconductive charging member having stable electrical resistance (Japanese Patent Application Laid-Open No. 2001-009958), and the like are reported.
A toner supplying roller having a surface layer of such a polyurethane foam is manufactured by, for example, the following method. First, a polyol component, an isocyanate component, a foaming agent, a foam control agent, and a catalyst are mixed and stirred, and the mixture is injected into a molding die for a toner supplying roller. The mixture is foamed in the die, and then the molded product is mold released, so that a toner supplying roller can be manufactured (Japanese Patent Application Laid-Open No. H09-274373 (pages 8 to 9)).
In manufacturing such a polyurethane foam layer, amine catalysts and organometallic catalysts are used as a catalyst used for the polymerization and curing of the polyurethane material. Specifically, the amine catalysts can include triethylenediamine, bis(dimethylaminoethyl)ether and N,N,N′,N′-tetramethylhexanediamine. The organometallic catalysts can include tin octylate, tin oleate, dibutyltin dilaurate, dibutyltin diacetate, tetra-i-propoxytitanium, tetra-N-butoxytitanium and tetrakis(2-ethylhexyloxy)titanium. Among these catalysts, the amine catalysts have advantages of good compatibility with water and longer toxicity and longer lifetime at the time of a premix than those of the organometallic catalysts. On the other hand, a large amount of the amine catalysts are used, and the amine catalysts may be a factor of image deterioration, for example, the amine catalyst remaining in the polyurethane foam layer gradually precipitates to contaminate a part, such as a developing roller, in contact with the toner supplying roller, and the toner.